A water-resistant portable apparatus of this type comprises a case in which an electroacoustic transducer is mounted, separated in a water-resistant manner by a deformable membrane from an inlet cavity, which is arranged in the case and in direct communication with the exterior.
Such portable apparatus are known from the prior art, particularly from EP Patent No. 0 899 635 filed in the name of the present Applicant, and incorporated herein by reference. This document discloses a water-resistant portable apparatus 1, shown in FIG. 5, comprising a case 2 in which there is mounted an acoustic transducer 21 so that it communicates in a water-resistant manner with the exterior of case 2 via acoustic energy. Acoustic transducer 21 is secured to a deformable membrane 15, separating it in a water-resistant manner from an inlet cavity 11 arranged in the case and in direct communication with the exterior.
A structure of this type has, however, several drawbacks. In the case of a piezo-electric type acoustic transducer, as shown, the control circuit housed in the case on a printed circuit board or PCB comprises, in particular, an amplifier with an integrated voltage multiplier, which has to be adapted to the transducer, and whose design on the PCB is more complex and consequently requires a larger surface.
Moreover, the connections between the piezo-electric transducer and a PCB are achieved by means of electrical wires, which requires difficult assembling operation on the transducer and operations for welding such wires.
Furthermore, the water-resistance of the structure shown is only guaranteed for the elements located above the deformable membrane. There is no device provided for sealing any electrical or electronic components located in the bottom of the case in a water-resistant manner.
The idea consisting in simply replacing the piezo-electric type acoustic transducer with an electrodynamic type acoustic transducer, i.e. a transducer with a moving conductor in which the moving part is a conductor through which a current, provided by an external source or induced by an external magnetic field, passes, raises difficulties as regards compactness in case, a dynamic transducer being relatively voluminous and whose thickness, in particular, is not negligible.